Writing a function to find a triangular number in python 2.7 -


i couldn't find answer searching , i've been working on 2 days , stumped. think confused on math. trying write function finds first n triangular numbers. 

def formula(n):     = 1     while <= n:         print i, '\t', n * (n + 1)/ 2         += 1     print

so example if type in formula(5) this:

 1       1  2       3  3       6  4       10  5       15

i got how make table going 1 through whatever number choose n.. can't figure out how make second part equal formula typed in n*(n+1)/2. logic going through this? everytime type in formula(5) example loop goes 1-5 returns same exact answer in right hand column way down 15. can't make start @ 1, 3, 6 etc on right hand side.

the comment observed computing n * (n + 1) / 2 instead of i * (i + 1) / 2 correct. can rid of having multiplication , division @ each step observing i-th triangle number sum of integers 1 i, @ each step have add previous triangle number. code below:

def formula(n):     ith_sum = 0     in xrange(1, n+1):         ith_sum +=         print i, '\t', ith_sum

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